With high-performance camshaft timing, the exhaust valves in different cylinders can be opened at the same time, overlapping at the end of the power stroke in one cylinder and the end of exhaust stroke in another. In a single-stage system employing a twin-scroll turbocharger, the exhaust manifold physically separates the channels for cylinders which can interfere with each other, so that the pulsating exhaust gasses flow through separate spirals (scrolls), which allows the engine to efficiently utilize exhaust scavenging techniques, which decreases cylinder gas temperatures and NOx emissions and improves turbine efficiency, reducing turbo lag. However, single-stage turbocharger systems do not provide the performance characteristics of a two-stage turbocharger system.
Accordingly, it is desirable to provide an exhaust manifold for a two-stage turbocharger system employing a twin-scroll turbocharger.